Answer: Blossom drop can be caused by a number of factors including high (or very cool) temperatures and perhaps most often, water stress. Regular watering should help and will help produce better quality tomatoes in any case. If the soil is very dry to begin with you may need to do some very deep watering at first -- dig down and see how far the water has reached -- and then after that you can do maintenance watering. These plants need as a rule of thumb an inch or so of water a week, more in hot or windy weather and when the plants are covered with tomatoes.
Finally, tomatoes do best in a rich organic soil that is evenly moist yet well drained. On the other hand, an excess of nitrogen can result in overly leafy plants (and an excess of notrogen early in the season may contribute to blossom drop). The best way to find out what to do with your soil is to run some basic soil tests and work from there; however, organic amendments such as peat moss and compost will always help the soil structure hold both air and water and this is good for the roots. The organic matter also breaks down over time and so needs to be replenished regularly, so you might consider adding some every year. Also, you should give strong consideration to rotating the location of your tomatoes simply to reduce the chances of pests or diseases carrying over from one year to the next.
If you are growing indeterminate tomatoes, I would expect you to still get a good crop. Determinate plants, however, are a bit less adaptable. Good luck with your tomatoes!
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